1. Field of the Invention
The present invention relates to organic germanium nanocolloids, to which technetium-99m (99mTc), a radionuclide, is labeled, a method of preparing the same and a use thereof as a spleen-imaging agent.
2. Description of Related Art
In general, nuclear medicine technologies for using nuclear power in medicine definitely require the use of a radiopharmaceutical. The radiopharmaceutical is prepared by selecting an appropriate material from among various kinds of radioisotopes generated when operating a nuclear reactor and processing it for use in the diagnosis or therapy of diseases to be administered to the human body. Such a radiopharmaceutical can readily and obviously detect metastasis of cancer that is difficult or impossible to diagnose using other techniques.
When a diagnostic radiopharmaceutical is administered to the human body, it accumulates in specific internal organs of the body depending on the diagnostic purposes. Thereby, diseases occurring in various internal organs of the human body may be diagnosed. That is, when the radiopharmaceutical accumulates in the internal organs, such as the brain, bones, thyroid gland, heart, lungs, liver, spleen, kidney, etc., an image of the γ-rays emitted from the radiopharmaceutical accumulated in such internal organs can be obtained using a γ-camera. In addition to the internal organs, the radiopharmaceutical may also accumulate in cancer, inflammation, blood, etc.
Further, a therapeutic radiopharmaceutical is composed of radionuclides, which emit stronger radiation capable of killing cells despite the lower permeability of the human body and have a relatively longer half-life, compared to diagnostic radiopharmaceuticals. Such radionuclides emit α-rays or β-rays. The radionuclides emitting α-rays are highly toxic and are not readily available. Besides, it is very difficult to label such radionuclides to other materials than diagnostic radionuclides. Thus, radionuclides emitting β-rays have been used to date as radiopharmaceuticals.
Methods of preparing radiopharmaceuticals for the diagnostic and therapeutic purposes include a method of labeling a specific radioactive isotope. An exemplary radioisotope widely used at present for labeling the diagnostic radiopharmaceutical is technetium-99m (99mTc). Since technetium has a relatively shorter half-life of 6 hours and emits only γ-ray energy of 140 keV suitable for obtaining a γ-image, it has low toxicity to the human body and high permeability thereto. Accordingly, it is most suitable for administrating technetium to the human body to obtain a desired image, thus being widely applied to diagnostic and therapeutic radiopharmaceuticals in nuclear medicine field (Silvia, S. J., John, D, L., Potential technetium small molecule radiopharmaceuticals, Chem. Rev. 99, 2205-2218, 1999; and Shuang, L., Edwards, D. S., 99mTc-labeled small peptides as diagnostic radiopharmaceuticals. Chem. Rev. 99, 2235-2268, 1999).
Meanwhile, the spleen is the largest lymphoid organ located under the left side of the rib cage. It is known that the spleen plays important roles in the human body such as destruction of blood cells, production of antibodies, lipoid metabolism, phagocytic function, bond marrow depression, etc. As a result of certain disease such as leukemia, lymphoma, typhoid and the like, the spleen may become very enlarged and may be ruptured easily by trauma.
Any of the technetium-labeled colloid preparations may be used for diagnosing any abnormality of the spleen. In the past, radiopharmaceuticals used for the spleen imaging include 99mTc-sulfur colloid, 99mTc-albumin colloid and 99mTc-red blood cell, which have been used to demonstrate the structure of the spleen and any abnormality therein (Atkins, H. L., Goldman, A. G., Fairchild, R. G., Radiology, 136, 501, 1980).
However, the radiopharmaceuticals for the spleen imaging have had a problem that their efficiencies are decreased more or less since the amount of the radiopharmaceuticals accumulated in the spleen is very small.
Germanium is one of the non-metallic elements, which can exist in valence states of 2 and 4. It has been known that metalloid germanium has widespread applications in various fields of electronics, nuclear sciences and medicines. In general, the germanium has a low toxicity, except for the tetrahydride germanium, and there have been reported few observations on toxicity of the germanium in the human body. However, since it is known that inorganic germanium compounds are more toxic than organic germanium compounds, it is undesirable to apply the inorganic germanium compounds to the human body.